In a mixture of cement and sand, sand is 30%. 200 kg of sand was added to the mixture

In a mixture of cement and sand, sand is 30%. 200 kg of sand was added to the mixture and its weight was 40%. How many kg of sand was in the mix initially?

Let’s assume that the initial mass of the mixture was x kg.

According to the condition of the problem, the proportion of sand was 30%, which means its mass was:

x * 30: 100 = 0.3 * x kg.

When 200 kg of sand was added to the mixture, the mass of the mixture became x + 200 kg, and the mass of sand in it was 0.3 * x + 200 kg.

Thus, according to the condition of the problem, we can compose the equation:

(0.3 * x + 200) / (x + 200) = 40/100,

0.3 * x + 200 = 0.4 * x + 80,

120 = 0.1 * x,

x = 1200 (kg).

This means that initially there was sand in the mixture:

1200 * 30: 100 = 360 (kg).

Answer: 360 kg.